"Neither Out Far Nor in Deep" sounds like a day at the beach.
No, seriously.
Okay, so it's not the kind of day that's full of sunscreen and snorkeling. Instead, it's a day for peacefully contemplating life's mysteries and maybe reconsidering our habit of turning our back to the land and the so-called real life it symbolizes. In that sense, the poem sounds calm and wavelike, while also shaking things up every once in a while in order point out a few habits that might need some revising.
The alternating rhyme scheme and iambic trimeter are some of the key techniques that make this poem sound like the sea. Whether we're alternating between "sand" and "land" or hearing the speaker's voice move down and up with syllabic patterns, there's no mistaking the wavelike sound of the poem. The speaker ends up sounding like that boat out in the middle of the sea that "keeps raising its hull" and crashing down on the surface. We're mesmerized by his wavy voice just as the people on the shore are mesmerized by the sight of the sea.